The invention relates to a carrier substrate for carrying objects subjected to elevated temperatures, the carrier substrate comprising at least a grid part and a border part.
The invention also relates to a method of manufacturing a selection electrode for a color cathode ray tube, said selection electrode comprising a shadow mask blank having a pattern of apertures, the method comprising the steps of providing patterns of apertures in a steel foil, cutting mask blanks from the steel foil, and annealing a stack of mask blanks at an elevated temperature, in which annealing step a carrier substrate of the above-mentioned type is used.
A carrier substrate for carrying objects subjected to elevated temperatures is known. In U.S. Pat. No. 4,427,396 a carrier substrate is described for use during an annealing step of mask blanks. Several manufacturing steps transform the mask blanks finally into selection electrodes for color Cathode Ray Tubes. To facilitate the subsequent deep drawing and obtain a grain size for good magnetic screening by the shadow mask, an annealing process is carried out on the blanks. To this end, a stack of blanks is placed on a carrier substrate and subjected to temperatures in the range of 600 to 880xc2x0 C. It appears that the lifetime of such carrier substrates is limited due to permanent deformation of the carriers occurring after several temperature cycles.
It is an object of the invention to provide a carrier substrate that has an improved lifetime.
A first aspect of the invention is characterized in that the carrier substrate comprises elements that are interconnected solely by interengaging connection portions.
Carrier substrates according to the state of the art comprise parts that are often connected to each other by welding or a similar connection technique. At elevated temperatures, the connection points appear to be sensitive to internal thermal stress, which leads to permanent deformation of the carrier substrate. The inventors have realized that internal stresses may be reduced by creating a connection without any additional connection means.
An embodiment of the invention provides a way of connecting elements to each other to result in a rigid frame that has as an additional advantage that the separate elements are easily replaced in case the frame needs to be repaired.
A further embodiment of the invention has the advantage that a rigid frame is obtained in which repair may easily take place.
A further embodiment of the carrier substrate according to the invention further improves the rigidity of the frame.
An embodiment of the invention further provides a proper selection of materials, which have a high yield strength, if the carrier substrate comprises a material selected from the group of materials molybdenum, tungsten, austenitic steel, ceramics or alloys of nickel and iron. Good results were obtained.
A second aspect of the invention provides a method of manufacturing a selection electrode for a color cathode ray tube, said selection electrode comprising a shadow mask blank having a pattern of apertures, the method comprising the steps of providing patterns of apertures in a steel foil, cutting shadow mask blanks from the steel foil, and annealing a stack of shadow mask blanks at an elevated temperature, in which annealing step a carrier substrate is used for carrying the shadow mask blanks, said carrier substrate comprising at least a grid part and a border part, characterized in that said carrier substrate comprises elements that are interconnected solely by interengaging connection portions.